One multimeter to detect all components

15. Identify the infrared receiver pin

Set the multimeter to R×1k, first assume that one pin of the receiving head is the ground terminal, connect it with the black test lead, and use the red test lead to measure the resistance of the other two pins respectively, and compare the two measured resistance values ​​(generally in the range of 4~7k Q). The one with smaller resistance is connected to the 5V power pin by the red test lead, and the other with larger resistance is the signal pin. On the contrary, if the red test lead is connected to a known ground pin, and the black test lead is used to measure the known power pin and signal pin respectively, the resistance values ​​are all above 15kΩ, the pin with smaller resistance is the 5V terminal, and the pin with larger resistance is the signal terminal. If the measurement result meets the above resistance value, it can be judged that the receiving head is intact.

16.Measurement of light emitting diodes

Take an electrolytic capacitor with a capacity greater than 100 "F (the larger the capacity, the more obvious the phenomenon), first charge it with the multimeter R × 100 block, connect the black test lead to the positive pole of the capacitor, and the red test lead to the negative pole. After charging, change the black test lead to the negative pole of the capacitor, and connect the LED to be tested between the red test lead and the positive pole of the capacitor. If the LED lights up and then gradually goes out, it indicates that it is good. At this time, the red test lead is connected to the negative pole of the LED, and the positive pole of the capacitor is connected to the positive pole of the LED. If the LED does not light up, swap its two ends and reconnect it for testing. If it still does not light up, it indicates that the LED is damaged.

17. Photocoupler detection

The multimeter should be set to the resistance R×100 range, and the R×10k range should not be selected to prevent the battery voltage from being too high and breaking through the light-emitting diode. Connect the red and black test pens to the input terminal, and measure the forward and reverse resistance. Normally, the forward resistance is tens of ohms, and the reverse resistance is several thousand ohms to tens of kiloohms. If the forward and reverse resistances are similar, it indicates that the light-emitting diode is damaged. Select the resistance R×1 range for the multimeter. Connect the red and black test pens to the output terminal, and measure the forward and reverse resistances. Normally, they are close to ∞, otherwise the light-receiving tube is damaged. Select the resistance R×10 range for the multimeter, and connect the red and black test pens to the input and output terminals respectively to measure the insulation resistance between the light-emitting tube and the light-receiving tube (if conditions permit, use a megohmmeter to measure its insulation resistance. At this time, the output rated voltage of the megohmmeter should be slightly lower than the withstand voltage allowed by the photoelectric coupler being measured). The insulation resistance between the light-emitting tube and the light-receiving tube should be ∞ normally.

18. Laser diode quality detection

Remove the laser diode and measure its resistance. Under normal circumstances, the reverse resistance should be infinite and the forward resistance should be between 20kΩ and 40kΩ. If the forward resistance exceeds 50kΩ, it means that the performance of the laser diode has deteriorated; if the forward resistance exceeds 90kΩ, it means that the tube is damaged and cannot be used anymore.